Method and apparatus for drying of paper, board or pulp webs, formed from cellulosicfibrous material



Feb. 22, 1966 HOOD ET AL 3,235,972

METHOD AND APPARATUS FOR DRYING OF PAPER, BOARD OR PULP WEBS, FORMEDFROM GELLULOSIC FIBROUS MATERIAL 2 Sheets-Sheet 1 Filed Jan. 9, 1963Feb. 22, 1966 N. R. HOOD ET AL 3,235,972

. METHOD AND APP TUS R ING OF PAPER, BO 0R PULP WEBS. FOR E FR CE LOSICFIBROUS MA IAL Filed Jan. 9, 1963 2 Sheets-Sheet 2 United States Patent3,235,972 METHGD AND APPARATUS FOR DRYING OF PAPER, BOARD 0R PULP WEBS,FORMED FROM CELLULOSI FIBROUS MATERIAL Norman Roy Hood, John Luckins,Charles Arthur Orr Sutherland, and Michael John Carpenter, Kenley,England, assignors to The British Paper and Board Industry ResearchAssociation, Surrey, England, a British company Filed Jan. 9, 1963, Ser.No. 250,398 Claims priority, application Great Britain, Jan. 18, 1962,1,972/62 16 Claims. (Cl. 34-9) This invention relates to the drying ofpaper, board or pulp webs, formed from cellulosic fibrous material.

Hitherto, the drying of continuous webs of cellulosic fibrous materialhas usually been effected by passing the web around a number of steamheated drying cylinders, there being endless drying felts which arearranged to press the web against the rotating cylinders during thedrying operation.

In accordance with the present invention, there is provided a method ofdrying paper, board or pulp webs of cellulosic fibrous material, whereina formed but undried, or not sufficiently dried, continuous Web of thematerial is passed, whilst being substantially vertically disposed,through a fluidised bed, the fluidised bed consisting of solid particlesundergoing fluidisation or pneumatic transport in a primary stream ofup-flowing gas in an inner region adjacent the web, and of particlesundergoing fluidisation in a secondary stream of tip-flowing gas in anouter region remote from the web, there being heating means for theheating of the particles of the fluidised bed to a temperature such thatthe water content of the web is reduced during passage of the webthrough the fluidised bed, the fluidised particles in the inner regionbeing more widely dispersed, or diluted to a greater extent, than thefluidised particles in the outer region.

The gas may be air or superheated steam or any other convenient gas. Thephenomenon of fluidisation depends on the upward forces imposed on theparticles by the upward stream of gas being substantially equal to theweight of the particles. The bed then expands somewhat allowing theindividual particles some freedom of movement. The system of particlesthus suspended in flowing gas shows a liquid-like behaviour and thesolids are consequently said to be fluidised. In particular the abilityof a gas stream, containing suspended solid particles, to transfer heatfrom one surface to another is much greater than the ability of the samegas stream when free from solid particles. Damp paper, board or pulpimmersed in or passed through a heated bed of gas fluidised particles isfound to dry much faster than in a gas stream at the same temperature.The rate of drying increases with a rise in bed temperature. The steamreleased by the drying of the paper, board or pulp is rapidly removedfrom the surface of the sheet and becomes mixed with the gas stream.

In accordance with a preferred example of the method, the meanconcentration of the particles in the inner region is less thanone-third of the mean concentration of the particles in the outerregion. Preferably, the mean concentration of the fluidised particles inthe outer region is between 80% and 99% of the bulk density of theparticles measured when the flow of fluidising gas is stopped. Theexpression mean concentration of the particles is intended, as usedherein and in the accompanying claims, to indicate the weight in poundsof the particles to be found at any time within a volume of one cubicfoot of the fluidised or pneumatically transported bed. It is to beunderstood that there may be local varia- "ice tions in concentrationwithin such unit volume due to, for example, bubbling in the outerregion or to eddying in the inner region, and that the specified meanconcentration is the average taken over a volume of one cubic foot.

The invention further provides apparatus for the drying of continuouswebs of paper, board or pulp, formed from cellulosic fibrous material,the apparatus comprising a container having openings at the top andbottom thereof to enable a web of the material to pass in asubstantially vertical path through the container and having in thelower part thereof inlet means for gas, such as air, for fluidising abed of solid particles within the container, the apparatus comprisingalso means adapted, during a drying operation, to provide at each sideof the web path, an inner region adjacent the web in which solidparticles of the fluidised or pneumatically transported bed, are morewidely dispersed, or are diluted, to a greater extent than fluidisedparticles in an outer region remote from the web path, said apparatusincluding also means for I heating the fluidised particles so that,during passage of the web through the container, the fluidised particlescan be maintained at a temperature for reducing the water content of theweb to the desired level. The heating means may comprise an array ofheating tubes which extend through opposite vertical walls of thecontainer and which are adapted to receive steam or other heating fluid,for the heating of the fluidised bed to a temperature of between 200 and900 F.

The gas inlet means may comprise at each side of the web, at least twoindependent inlets including a first inlet extending along the loweropening and through which a gas stream can be forced to preventparticles falling through said lower opening and to provide an overallupward movement and an adequate but lower concentration of the particlesin the inner region adjacent to the web surface, and a second inlet inthe form of a porous or perforated plate to the underside of which gascan be supplied to ensure adequate fluidisation of the bed in the outerregion remote from the web, so that said outer region will contain ahigher concentration of the particles. In this arrangement, the verticalflow rate of gas per unit cross sectional area is greater in the regionsadjacent to the web than in the regions remote from the web. Inconsequence, there is an overall circulation of the fl-uidised particleson each side of the web, as well as their random motions, whichcirculation is upwards in the region adjacent to the web until theparticles reach the top of the baffles where they move outwards to theregion remote from the web and therein move downwards past the heatingmeans, until they return inwards to the region adjacent to the web bypassing through a gap be tween the lower end of the bafiies and theporous or perforated floor of the container.

The region adjacent to the web may be constricted at two or more levelsby pairs of horizontal projections, one of each pair on the inner wallof each baflle, into a plurality of independent pockets located oneabove another on each side of the web, by which constrictions theupwardly moving fluidised particles are brought into closer proximitywith the web which is being dried.

For a better understanding of the invention and the method by which itmay be performed, the same will now be described, by way of example,with reference to the accompanying diagrammatic drawings, in which:

FIGURE 1 is a diagrammatic longitudinal sectional view of dryingapparatus according to one constructional embodiment of the invention,and

FIGURE 2 is an elevational view of the apparatus.

Referring to FIGURE 1, the drying apparatus illustrated comprises anupright tank or container 1 having an enlarged lower section 2, anintermediate section 3 which is of rectangular horizontal cross-sectionthroughout, and an upper or top section 4. The lower section 2 of thecontainer has in the base thereof a central transversely extendingopening 5 through which a web of paper material, indicated by a brokenline at A, can be led into the container for drying purposes. The uppersection 4 also has a central transversely extending opening 6 throughwhich the web or paper material is led out of the container.

The lower section of the container is provided also with two primary gasinlet elements 7, 8 disposed one at each side of the lower opening 5.These primary gas inlets 7, 8 communicate with a pressure box (notshown) which is supplied with gas, such as air, under pressure. Theprimary gas inlet slots 7, 8 extend the full width of the container.

The lower section of the container also includes at each side of the webA and further therefrom than the primary gas inlets 7, 8, a porous orperforated floor 9 comprising porous ceramic tiles or metal platespierced by a large number of small holes. Beneath the porous orperforated floor 9 at each side, there is disposed a secondary pressurebox 10 adapted to be supplied with compressed gas, such as air, throughan associated inlet 11, these secondary gas pressure boxes 10 beingseparated from or 'sponding projections 16 of the two baflles arelocated at the same height, so that each pair of projections makes aconstriction in the inner regions adjacent to the web.

independent of the pressure boxes associated with the two primary gasinlets 7, 8. Valve means (not shown) are provided for controlling thepressure of the air or other gas which flows through the primary andsecondary inlets into the container.

Above the floor and at each side of the Web A, there is provided withinthe enlarged lower section 2 of the container, heating means which, inthe present embodiment, takes the form of an array of heating tubes 12,these tubes 12 being located in laterally outer regions 13 at oppositesides of and remote from the web A. The tubes 12 extend through theopposite vertical end walls of the container and the ends of the tubesassociated with one wall are effectively connected to a source of steamunder pressure, the steam being, for example, at a temperature of about350 C. The other ends of the tubes are conmeet to steam traps (notshown). It will be understood that the heating means may take the formof electrical heating elements or any other convenient means; also, theheat exchange surfaces of the heating means may be finned or extended inother desired manner.

Baflles 14 are provided within the container at each side of the movingweb A so as to divide the fluidised bed into two substantiallyindependent regions, comprise ing the outer regions 13 which are remotefrom the web, and inner regions 15 which are adjacent to and at oppositesides of the web. The baflles 14 comprise two substantially verticalplates spaced apart from opposite sides of the web A and parallel to theside walls of the container. The plates 14 correspond in width to theinterior of the container and are fitted at the opposite edges thereofclosely against the vertical end walls of the container.

In the present embodiment, the intermediate section 3 of the containeris of reduced width and this merges at its upper end into laterallyoutwardly and upwardly curved wall parts of the upper section 4. Thus,at each side of the web A, the outer region of the fluidised bed, willbe somewhat narrower as shown at 21, in the inter-, mediate section ofthe container than in the bottom and top sections thereof.

The outer faces of the baffles 14 directed towards the outer regions ofthe fluid bed are substantially flat, but the inner faces bounding theinner regions 15 adjacent the web are provided with horizontallyextending projections 16. In the illustrated embodiment, each bafile 14carries on its inner face a multiplicity of the horizontally extendingprojections 16, these each being substantially of right-angledtriangular shape in cross section and disposed with the facecorresponding to' the hypotenuse of the triangle secured to the adjacentbaffle. The corre- The projections may be of rounded or of any otherconvenient shape in cross-section.

Each bafl'le carries an outwardly and downwardly inclined deflector 17which extends within the lower section 2 of the container and is adaptedto deflect the particles of the fluidised bed laterally outwardly, intothe laterally extended parts of the lower section of the container. InFIGURE 1, the normal level of the sand before fluidisation is indicateddiagrammatically at 18.

The bafl'les 14 extend upwardly into the upper section 4 of thecontainer where the top edges of the baffles are curved outwardly anddownwardly to form exhaust ducts 19 which cooperate with the curved wallparts of the top section 4 of the container, to define passages 20 ateach side of the web through which the fluidised particles can pass fromthe inner regions 15 into the outer regions at the outer sides of thebafiles 14. Each bafile 14 extends at its lower end into the lowersection 2 of the container, the lower edges of the two bafiles beingspaced a short distance above the floor of the container, to provide agap 22 through which the fluidised particles can pass from one region toanother. The lower end of each baffle is extended downwardly by means ofan adjustable shutter or damper 23 to allow the lower gap 22 to bevaried to provide control, as required, in the passage of particlesbetween the two regions at the bottom of the container.

Means is provided in the top section of the container for the dischargeof the upwardly flowing stream of air or gas employed to fluidise thebed, and for the discharge also of steam which is produced by the dryingof the web and which becomes mixed with the gas stream. Thus, for theescape of spent air, or gas, and steam from the container, there areprovided the exhaust ducts 19 which extend through the opposite verticalend walls of the container, these ducts and the top section 4 of thecontamer being shaped to direct the particles back to the outer regionswhile permitting escape of the spent air or gas from the container.

As shown in FIGURE 1, the top section 4 of the contamer is of graduallyincreasing width so that, during operation of the fluidised bed, theupward velocity of the gas stream will tend to be reduced, therebyfacilitating the return of the particles passing upwardly from the innerregions 15 and over into the outer regions of the fluidised bed. Forthis purpose, there is also provided in the inner section 4 of thecontainer, transversely extending deflector plates 24. If desired,electrically operated fan means may be provided at the top of thecontamer for directing particles back to the fluidised bed. Moreover,the exhaust ducts may be connected to a centrifugal separator (notshown), adapted to remove any particles still suspended in the gasstream, means being connected in circuit with the centrifugal separatorto enable the issuing gas stream either to be exhausted to atmosphereor, alternatively, subjected to heat exchange and particle removingprocesses, to enable the gas to be recycled through the primary andsecondary gas supplies.

Where, as in the present embodiment, it is intended that the web A to bedried shall move vertically upwards through the container, means isprovided for removing from the web any particles adhering thereto andcarried up through the container by the web. Thus, referring to FIGURE1, there are provided downwardly directed jets of gas, such as air,arranged to impinge on the web surfaces. These downwardly directed gasjets issue from a pair of horizontal slot-like inlets 25 arranged at thetop of the apparatus at opposite sides of the upper web opening 6, theseupper gas inlets 25 being similar to the primary gas inlet 7 provided atthe lower end of the container.

The adjustable shutter or damper 23 allows the gap at the lower ends ofthe baflles to be varied between, for

example, half an inch when the shutter or damper is fully opened andabout the mean diameter of the particles of the fluidised bed, whenfully closed. Alternatively, the particles may be allowed to pass fromthe outer to the inner regions through one or more pipes or holes formedin the baflles and dimensioned and spaced according to the desired rateof flow of the particles from one region to the other.

In the present embodiment, the container 1 comprises two relativelydisplaceable or separable parts 26, 27 (FIG- URE 2) adapted to be joinedtogether in the vertical plane of the web A. The left-hand part 26 islocated fixedly in a vertical position and secured against upper andlower abutments 28, 29. The right-hand part 27 of the container isarranged for translational displacement in the direction of arrows X(FIGURE 2) away from and towards the fixed part 26. For this purpose,the casing part 27 is formed with vertically spaced upper and lowerbearing supports 30, 31 in each of which there is mounted an associatedtransversely extending shaft 32 carrying pinions 33. Spaced laterallyfrom the movable part 27 of the container, there is disposed a verticalsupport or wall 34 to which are secured upper and lower bracket 35, 36each provided along its upper edge with a rack 37 engageable by theassociated pinion 33. Each of the shafts 32 carries a drive sprocket 38engaged by a driving chain 39. The arrangement is such as to maintainthe movable part 27 of the casing in a vertical position during itsmovement to and from the associated fixed part 26. Power means is alsoprovided for actuating the movable part 27 of the container. In thepresent embodiment, the power means comprises a double acting fluidpressure operated piston and cylinder device 40, the piston of which isoperatively connected by connecting rod means 41 to the container part27. The piston and cylinder device 40 is provided with air admissionpipes 42, 43, so that, by introducing air under pressure through thepipe 42, the piston and its rod 41 can be displaced to move theright-hand part 27 of the container into an open position removed fromthe relatively fixed part 26 and, by introducing air through the pipe43, the movable part 27 can be displaced into a closed position adjacentthe fixed part 26. The operating mechanism and the chain-sprocket drivemeans, is such as to ensure parallel movement of the casing part 27relatively to the fixed part 26.

To prepare the apparatus for a drying operation, the piston and cylinderdevice 40 is operated to separate the two parts of the container, asdescribed with reference to FIGURE 2, to facilitate the location of theweb A in the medium plane of the apparatus. Upon closing of thecontainer parts, the web which is guided "by upper and lower guide rolls42, 43, will extend vertically between the upper and lower openings 5,6.

The outer regions 13 in the lower section of the container, are chargedwith particles to the level indicated at 18, and gas, such as air, issupplied to the primary and secondary inlets to fluidise the particles.The valves associated with the two sources of gas are so controlled thatin the two outer regions, the mean concentration of the fluidisedparticles, will be between 80% and 99% of the bulk density of theparticles when the flow of fluidising gas is stopped. The fluidisedparticles passed through the lower gaps 22 into the inner regions wherethe primary gas supply is such that the particles undergo fluidisationor pneumatic transport, the particles in the inner regions adjacent theweb, being more widely dispersed, or diluted to a greater extent, thanthe fluidised particles in the outer regions. In the present example,the particles consist of rounded grain sand. In the two inner regionsthe particles have a mean concentration which is less than onethird ofthe mean concentration of the particles in the two outer regions. Thus,there may be a concentration of about 90 lb./cubic foot in the outerregions and less than about 30 lb./ cubic foot in the inner regions. Thearrangement is such that there is produced a circulation in which theparticles in the two outer regions move slowly downwardly incounter-direction to the upward flow of the air or gas from thesecondary supply, and the particles in the two inner regions 15 are in aborderline condition between fluidisation and a pneumatic transport ofthe bed. Thus, in the inner regions the particles move upwardly betweenthe bafiles 14 and then outwardly over the tops of the bafiles so as tore-enter the outer regions. The particles then pass downwardly forpassage over the heating means and thence through the lower gaps 22 intothe inner regions.

The speed of the moving web may be [from zero to 5,000 feet per minuteor more depending on the paper, board or pulp web machine on which thedrying apparatus is being used. The gas may be supplied to the slot-likeprimary inlets 7, 8 at a pressure of up to 15 lbs. per square inchgauge, and supplied to the pressure boxes 10 of the secondary supply ata pressure of up to 10 lbs. per square inch gauge, such that thepressure at any height within the regions 13 containing the heatingmeans is substantially equal to the hydrostatic pressure of thefluidised particles therein. The temperature of the fluidised bed may bebetween 200 and 900 F. to suite the particular nature and speed of theweb which is to be dried.

The particles, which should be free from sharp edges and stable at thetemperatures to be used, may be between 1.0 millimetre and 0.1millimetre in size, preferably .between 0.5 and 0.2 mm. They may, forexample, be rounded grain sand. Alternatively, the particles may consistof small glass balls known as ballotini of a size between and 500microns.

The distance between the 'baflles may be from 1 to 6 inches but thisspacing is constricted at the necks between the opposed triangularprojections 16, to a distance of Lfrom about A to 2 inches. Theprojections may be spaced apart vertically by a distance of from 1 to 12inches.

Should it be necessary during operation of the apparatus, to obtainaccess to the interior of the apparatus, it is necessary merely to shutoff the secondary supply of air or gas to the porous floor 9 of thecontainer so that, in the two lower outer regions 13, the particles willno longer be fluidised and the flow of particles from the outer regions13 through the lower gaps 22 into the adjacent inner regions 15, willalso be arrested. The supply of primary air or gas to the inner inlets7, 8 may be continued to drive the relatively thinly dispersed ordiluted particles within the inner regions 15, upwardly and over thebaflles 14 into the adjacent outer regions. This can be facilitated byincreasing the flow of air or gas through the primary gas inlets 7, 8.-The supply of primary air or gas is then shut-off and the two halves 26,27 of the container separated by operating the piston and cylinderdevice 40. The drive mechanism is such that the opening of the containercan be carried out smoothly and with the two parts maintainedsubstantially parallel to each other. Also substantial loss of particlesis avoided since substantially all of the particles are returned to theouter regions 13 of the lower section 2 of the two container parts,before opening of the container.

A moving continuous web of paper, board or pulp may be dried by acombination of conventional means, for example, steam heated dryingcylinders, and one or more fluid bed drying apparatus arranged in seriesto form the drying section of the machine. While the fluid bed dryingapparatus is found to be very effective in evaporating water from theweb, it will be necessary in the case of paper and board to makeprovision for smoothing and flattenig the web by conventional means. Itis found that by the additional drying effect of the fluidised bed or'beds, the drying section of a continuous paper, board or pulp machinecan be run at a greater speed without increasing the overall length ofthe machine.

The following Example will serve further to illustrate the drying methodemploying the aforedescribed apparatus.

Example A damp continuous web one foot wide of Kraft papermaking pulpobtained from the wet-end of a paper forming device, was led in anupward direction through a fluidised bed drying apparatus at a speed of240 feet per minute. The particles consisted of rounded grain sand of 40to 60 mesh size and were heated to 300 C. in the outer regions of thecontainer remote from the web path, the heating means consisting ofelectric heating elements dissipating 62 kilowatts. The particles wereallowed to pass continually from the outer regions 13 into the innedregions 15 disposed between the two bafiles 14, the arrangement beingsuch that there was an overall upward movement of the particles withinthe inner region in contact with the moving web A. The air supplies wereso adjusted that the mean concentration of the particles in contact withthe moving web in the inner region, was 6 lbs. per cubic foot, and thatin the outer regions where the heating elements were situated, the meanconcentration was 90 lbs. per cubic foot.

Upon severing of the web passing through the apparatus, for the purposeof taking samples from the web, the supply of air to the outer regions13 of the container was stopped, thereby preventing the passage of sandfrom the outer regions into the inner regions. The air supply to theinner regions was continued so that the inner regions were rapidlyemptied of sand. The movable part 27 of the container was then operatedby the device 40 to split the two parts of the container in the verticalplane of the web, for the purpose of facilitating the re-threading andproper location of the web between the container parts. The two parts orhalves were then brought together again and air supplied to re-fluidisethe particles.

It was found that the water to solids ratio of the web entering theapparatus was 1.83 and that of the web leaving the apparatus was 1.58.The continuous web employed was of 132 grams per square metre dry basisweight. It was found also that in passing through the apparatus, waterwas removed from the paper web at a rate of 97 lbs. per hour.

We claim:

1. A method of drying cellulosic fibrous material comprising: providinga bed of solid particles; fluidizing said particles in the form of avertically extending inner region and a vertically extending outerregion by passing a primary stream of fluidizing gas upwardly throughsaid inner region and by passing a secondary stream of fluidizing gasupwardly through said second region; passing a continuous web of thematerial to be dried substantially vertically through said inner region;dispersing the particles more widely in said inner region than in saidouter region; and heating the fluidized particles whereby the watercontent of the web is reduced.

2. A method as in claim 1 which includes passing said web upwardlythrough said inner region; maintaining the velocity of said primary gasstream sufficiently high to move the particles in said inner regionupwardly and maintaining the velocity of said secondary gas stream lowerthan the velocity of said primary gas stream to cause the particles insaid outer region to move downwardly, said method including the step ofproviding vertically spaced constrictions in said inner 'region to formsubstantially independent pockets in said inner region, so that said webpasses vertically through said pockets as it passes upwardly throughsaid inner region.

3. Drying apparatus for the drying of webs of cellulosic fibrousmaterial comprising: a container having an upper opening at the top anda lower opening at the bottom; a mass of solid fluidzable particles insaid container; means for fluidizing said particles in the form of avertically extending outer region and a vertically extending innerregion in which the particles are dis.-

persed more widely than in said outer region, said means includingbaffle means in said container defining said regions, primary .gas inletmeans for introducing an upward flow of gas into said inner region andsecondary gas inlet means for introducing an upward flow of gas intosaid outer region; means for guiding a web to be dried along a pathsubstantially vertically through said inner region; and heating means insaid container for heating said particles.

4. Drying apparatus for drying webs of cellulosic fibrous materialcomprising: a container having a web inlet opening in its bottom and aweb outlet opening in its top; means including two laterally spacedapart baffles forming within said container a centrally disposed innerregion between the bafiles and laterally outer regions with the outersides of the baflles; means for guiding a web of cellulosic fibrousmaterial substantially vertically through said inner region from thelower inlet opening to the upper outlet opening; a mass of solidfluidizable particles in said container; means for fluidizing theparticles in said inner region for movement in an upward direction, saidmeans including primary gas inlet means at the lower part of said innerregion; means for fluidizing the particles in said outer regions formovement in a downward direction, said means including secondary gasinlet means at the lower part of said outer regions; and heating meansin said container for heating said particles.

5. Apparatus as in claim 3 wherein said container is formed of tworelatively movable parts, said apparatus further including means formoving said parts relatively one to another into an open position topermit the web to be located vertically in said inner region, saidprimary gas inlet means including a gas inlet element associated witheach container part.

6. A method as claimed in claim 1, which includes moving the particlesupwardly in said inner region adjacent the web, and moving the particlesdownwardly in said outer region remote from the web.

7. A method as claimed in claim 1 which includes introducing air underpressure from a primary source to form said primary stream of fluidizinggas, and introducing air under pressure from a second source to formsaid secondary stream of fluidizing gas.

8. A method as claimed in claim 1 which includes introducing superheatedsteam from a first source to constitute and primary stream of fluidizinggas, and introducing super-heated steam from a second source toconstitute said secondary stream of fluidizing gas.

9. A method as claimed in claim 2 which includes maintaining theparticles in said inner region at a mean concentration which is lessthat one-third of the mean concentration of the particles in said outerregion.

10. A method as claimed in claim 9, which includes maintaining theconcentraion of the particles in said outer region between and 99% ofthe bulk density of the particles as measured when the flow offluidising gas is stopped.

11. Apparatus as claimed in claim 4, wherein said primary gas inletmeans extends along the lower opening for the web and is independant ofeach secondary gas inlet means, each primary inlet means being disposedto direct a primary gas stream upwardly to prevent particles fallingthrough said web inlet opening and to provide an overall upward movementof the particles in said inner region adjacent to the web surface, andwherein each secondary gas stream through said porous plate and meansfor supplying a secondary gas stream through said porous plate for thefluidisation of the particles in said outer regions at a higherconcentration than the particles in said inner region.

12. Apparatus as claimed in claim 4, wherein said bafilesaresubstantially vertically disposed and include gaps at their top andbottom to permit the passage of the fluidised bed particles from theinner region to the adjacent outer regions, during a drying operation.

13. Apparatus as claimed in claim 4, wherein said container has anenlarged lower section, and wherein said heating means comprises anarray of heating tubes disposed in said outer regions and extendingbetween opposite side walls of said lower section, there being means forsupplying said heating tubes with a heating medium for the heating ofthe fluidised bed to a temperature of between 200 and 900 F.

14. Apparatus as claimed in claim 12, including shutter means forcontrolling the flow of particles through the lower gap in each bafile.

15. Apparatus as claimed in claim 12, including projections provided onand extending across the opposed surfaces of said baffies, theprojections on each baffle being spaced apart from one another and thecorresponding projections on said two bafiles being located opposite oneanother to sub-divide the space between said bafiles into a plurality ofsubstantially separated pockets.

16. Apparatus as claimed in claim 5, wherein said References Cited bythe Examiner UNITED STATES PATENTS 2,785,478 3/1957 Audas et al. 34-92,938,276 5/1960 Doleman et al 34-95 3,061,941 11/1962 Gay et al. 34-953,061,943 11/1962 Bennett et al 3495 FOREIGN PATENTS 887,216 1/1962Great Britain.

20 WILLIAM F. ODEA, Acting Primary Examiner.

NORMAN YUDKOFF, Examiner.

1. A METHOD OF DRYING CELLULOSIC FIBROUS MATERIAL COMPRISING: PROVIDINGA BED OF SOLID PARTICLES; FLUIDIZING SAID PARTICLES IN THE FORM OF AVERTICALLY EXTENDING INNER REGION AND A VERTICALLY EXTENDING OUTERREGION BY PASSING A PRIMARY STREAM OF FLUIDIZING GAS UPWARDLY THROUGHSAID INNER REGION AND BY PASSING A SECONDARY STREAM OF FLUIDIZING GASUPWARDLY THROUGH SAID SECOND REGION; PASSING A CONTINUOUS WEB OF THEMATERIAL TO BE DRIED SUBSTANTIALLY VERTICALLY THROUGH SAID INNER REGION;DISPERSING THE PARTICLES MORE WIDELY IN SAID INNER REGION THAN IN SAIDOUTER REGION; AND HEATING THE FLUIDIZED PARTICLES WHEREBY THE WATERCONTENT OF THE WEB IS REDUCED.